$format message handler for web API OData.

DollarFormatHandler.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Threading;
using System.Threading.Tasks;
using System.Web.Http;
using System.Web.Http.Hosting;
using System.Web.Http.OData;
using System.Web.Http.OData.Builder;
using Microsoft.Data.Edm;

namespace NewSoTests
{
    class Program
    {
        static void Main(string[] args)
        {
            ODataConventionModelBuilder builder = new ODataConventionModelBuilder();
            builder.EntitySet<Customer>("Customers");
            IEdmModel model = builder.GetEdmModel();

            HttpServer server = new HttpServer();
            server.Configuration.MessageHandlers.Add(new DollarFormatHandler());
            server.Configuration.Routes.MapODataRoute("default", "", model);

            HttpClient client = new HttpClient(server);
            var response = client.GetAsync("http://localhost/Customers?$format=application/json;odata=fullmetadata").Result;

            Console.WriteLine(response.Content.ReadAsStringAsync().Result);
            response.EnsureSuccessStatusCode();
            Console.ReadKey();
        }
    }

    public class DollarFormatHandler : DelegatingHandler
    {
        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            var queryParams = request.GetQueryNameValuePairs();
            var dollarFormat = queryParams.Where(kvp => kvp.Key == "$format").Select(kvp => kvp.Value).FirstOrDefault();

            if (dollarFormat != null)
            {
                request.Headers.Accept.Clear();
                request.Headers.Accept.Add(MediaTypeWithQualityHeaderValue.Parse(dollarFormat));

                // remove $format from the request.
                request.Properties[HttpPropertyKeys.RequestQueryNameValuePairsKey] = queryParams.Where(kvp => kvp.Key != "$format");
            }

            return base.SendAsync(request, cancellationToken);
        }
    }

    public class Customer
    {
        public int ID { get; set; }

        public string Name { get; set; }
    }

    public class CustomersController : ODataController
    {
        [Queryable]
        public IEnumerable<Customer> GetCustomers()
        {
            return new[] { new Customer() };
        }
    }
}